A new paleomagnetic pole of Lower Cretaceous units from Sierra Chica de Córdoba, Argentina, and the Middle Jurassic-Cretaceous APW path of South America

GEUNA, SILVANA

Uppsala

Congreso; IAGA 8th Scientific Assembly; 1997

Four localities that yielded paleomagnetic poles on Early Cretaceousvolcanics of Sierra Chica de Córdoba, Argentina (31.5°S, 64.4°W) have beenrevisited: Cerro Colorado, Rumipalla, El Salto-Almafuerte and Rio Los Molinos.New sampling sections have been added to this revision. The conclusions are: 1)Previous VGPs were often based upon biased magnetizations, because of viscouscomponents carried by multidomain magnetite. 2) The primary magnetization iscarried by finer (titano)magnetite, which is present in basalts with higherdegree of deuteric oxidation. Deuterism has been simultaneous with cooling oflava flows. Conglomerate test for this component is positive. Localities withreliable structural corrections (this excludes El Salto- Almafuerte) andsimilar age determination (this excludes Rio Los Molinos) were used to computea new Sierra Chica de Córdoba PP: Lat. 86.0°S; Long. 75.9°E (A95 3.3, K=35, N=55). This PP based on 23 localities supersedes poles mentioned above. The newand previous Rio Los Molinos data (not included in Sierra Chica PP) should notbe used because they belong to six independent spot-readings of the ancientfield, all of them of reverse polarity. The incorporation of Sierra Chica PPgreatly improves the Middle Jurassic-Cretaceous APW path of South America.